1. Field of the Invention
The present invention relates to a fullerene derivative, a method of manufacturing a fullerene derivative and a solar cell.
2. Description of the Related Art
Fullerenes, prepared first in 1985, are a third carbon allotrope in which 60 or more carbon atoms are bonded in a spherical shape. Fullerenes, typically as C60, C70, C76, C78, C82, C84 or the like, have been marked as new functional materials for electronic components, drugs, cosmetics or the like because of their specific molecular shapes.
For methods of manufacturing fullerenes, arc discharging, resistance heating, laser vaporization, a combustion method, thermal decomposition or the like are known. By any methods, soot including fullerenes are generated. The fullerenes capable of being dissolved in organic solvent such as C60, C70, C76, C78, C82, C84 or the like are obtained by extracting the soot by the organic solvent. Further, by chemically-modifying these fullerenes to obtain fullerene derivatives, it is possible to improve solubility of the fullerene derivatives to organic solvent or water.
Conventionally, fullerene derivatives modified with a substituent group such as a hydrocarbon group or the like have been reported. Among these, fullerene derivatives modified with an amino group are very interesting materials expected to be applicable for various materials because they have a high solubility to organic solvent or the like and it is possible to directly control an electron accepting function of the fullerene.
Patent Document 1 disclose a method of manufacturing fullerene derivatives modified with amino groups by adding amine compounds to a fullerene. However, according to the method disclosed in non Patent Document 1, a fullerene derivative added with six amino groups and six hydrogen atoms is obtained. Further, according to the method disclosed in Patent Document 1, only a fullerene derivative modified with four amino groups and one epoxy group, and a fullerene derivative modified with five amino groups and one hydroxyl group are obtained.
It has been difficult to selectively add one amino group to a fullerene derivative. When fullerene derivatives are used for diodes for organic thin film solar cells or the like, the number of substituent groups may be two in order to retain original characteristics of fullerenes such as an electron accepting function or an electron transporting function. Further, it is desirable to introduce not only an amino group but also another substituent group to fullerenes in order to precisely control the electron accepting function of the fullerenes.
Patent Document 2 discloses a method of manufacturing a fullerene derivative including a phenyl group and a phenylamino group by applying aniline to fullerenol as a source material. However, the obtained fullerene derivative includes an aryl group such as a phenyl group, a tolyl group or the like. Generally, the fullerene derivative substituted by the aryl group has a low solubility. Thus, it was difficult to form a thin film of a fullerene derivative using a solution process such as a printing method or the like for an organic thin film solar cell or the like.
Patent Document 3 discloses a method of manufacturing a fullerene derivative including an alkyl group and an amino group. However, the alkyl group and the amino group are limited to be provided at 1,2 position and it was impossible to manufacture a fullerene derivative in which the alkyl group and the amino group are provided at 1,4 position. It means that a degree of freedom in a molecular design was limited. As will be explained later, 1,4-difunctionalized fullerene derivatives possessing two identical or unsymmetrical functional groups on 1,4-position of a fullerene core such as C60 or the like are expected to offer various functional properties.